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Retroperitoneal fibrosis (RPF) is a well described clinical entity that is being diagnosed with increasing frequency. RPF is characterized by replacement of the normal tissue of the retroperitoneum with fibrosis and/or chronic inflammation. However, aetiology, clinical presentation and radiological appearance in many cases are protean.

Up to 15% of patients have additional fibrotic processes outside the retroperitoneum. In the abdomen, RPF may spread contiguously to involve multiple structures in both the retroperitoneum and the peritoneal cavity or multiple non-contiguous sites may be involved. We retrospectively reviewed 30 patients (19 male, 11 female; age range 28-79 years) with biopsy proven RPF. Although we found RPF most commonly as an isolated fibrotic plaque in the lower lumbar region (18 patients), 12 patients (40%) presented with RPF in atypical locations (4 peripancreatic, 1 periduodenal, 7 pelvic). The RPF was non-malignant in 24 patients (21 idiopathic, 2 perianeurysmal, 1 ergot-derivative treatment) and malignant in six cases.

We present a pictorial review of the varied appearances of RPF, concentrating on atypical sites. The radiological differential diagnosis and its appearance with various imaging modalities are discussed. Current concepts with respect to management, prognosis and treatment are summarized.